This invention relates to a hydraulic cylinder with a potentiometric position-sensing transducer.
In hydraulic controls technology, it is often desirable to obtain feedback signals representing the operating position of a hydraulic cylinder. U.S. Pat. No. 3,726,191 discloses one solution to this problem. The '191 cylinder has a resistance and conductor element support reciprocally received in a piston rod bore. A conductive wiper assembly is carried for movement with the piston and rod. However, the transducer construction of the '191 patent requires a relatively large transducer cross section which displaces a large volume of hydraulic fluid as the cylinder rod moves with respect to the transducer assembly. The bore required in the cylinder rod to accommodate such a transducer of large cross section and to provide an escape path for displaced hydraulic fluid is so large as to prevent its use in many hydraulic cylinders where compact size is required. Furthermore, the wiper contacts of the '191 patent are suspended in the fluid escape path, allowing flow forces to vibrate or bend the contact leaf, resulting in operation noise and loss of signal, respectively. Finally, the element support is supported only at one end by a plastic sealing element which is subject to mechanical stress and failures.